Project Summary
The rise of antibiotic resistance among healthcare associated pathogens has created a public health
emergency and is a major challenge to the provision of effective medical care. Multidrug-resistant (MDR)
Pseudomonas aeruginosa is labeled as a serious threat by the Centers for Disease Control and Prevention,
and disproportionately impacts medically vulnerable patients such as those in the intensive care unit. The
emergence of resistance to front-line antibiotics, including carbapenems and recently introduced ß-lactam/ß-
lactamase inhibitor combinations, has led to the use of alternate regimens with decreased efficacy and
increased toxicity. Cefiderocol (FDC) is a novel siderophore cephalosporin that retains in vitro activity against
MDR-P. aeruginosa. This antibiotic mimics the iron binding molecules P. aeruginosa requires for growth, and is
actively transported into the periplasmic space by proteins on the outer membrane of the bacteria called TonB
dependent receptors (TBDR). Resistance to FDC has been linked to a loss of expression of these TBDRs in
clinical isolates of P. aeruginosa. Further, an analysis of genomes of P. aeruginosa collected before the
approval of FDC found that mutations predicted to lead to decreased expression of TBDR genes were present
in carbapenem-resistant isolates. Using population analysis profiles (PAP), several strains of P. aeruginosa
with TBDR mutations showed heteroresistance to FDC, or growth of a small population of bacteria at antibiotic
concentrations above the clinical resistance breakpoint despite testing susceptible on standard susceptibility
testing. In two major specific aims, this proposal will investigate the hypothesis that mutations in TBDR genes
are present across clinical isolates of P. aeruginosa from diverse geographic areas and lead to the emergence
of resistance on exposure to FDC. In the first aim, the prevalence of TBDR gene mutations will be evaluated in
a collection of nearly one thousand carbapenem-resistant P. aeruginosa from the Prospective Observational
Pseudomonas study (POP). Alterations in this pathway will be linked to FDC susceptibility testing results, an
assessment of heteroresistance using PAP, and clinical features of P. aeruginosa colonization and infection. In
the second aim, we will investigate strategies to understand and mitigate the emergence of resistance
associated with TBDR mutations. First, a disk diffusion-based method to identify heteroresistant isolates will be
developed as a screening test for the clinical microbiology laboratory. Second, a hollow fiber infection model
simulating human pharmacokinetics of FDC will be used to evaluate the emergence of FDC resistance at
clinically relevant drug concentrations. This proposal will provide important information on the distribution and
prevalence of mutations associated with resistance to FDC in P. aeruginosa. The development of an assay to
identify isolates at risk of resistance, and an understanding of the mechanism by which resistance emerges at
human drug exposures, can form the basis for rational therapeutic use of FDC at the patient bedside.
